Sulfonated asphalts are conventionally prepared by contacting the asphalt with a suitable sulfonating agent to produce sulfonic acids, neutralizing the sulfonic acids with a suitable neutralizing agent to produce sulfonated asphalt, separating the sulfonated asphalt from unreacted materials and any carrier materials or diluents, such as water from an aqueous acid or neutralizing agent, and drying the thus separated sulfonated asphalt. The dried sulfonated asphalt can then be utilized in the preparation of drilling fluids, such as aqueous, oil-base, and emulsion-types. Such drilling fluids have been found to have excellent rheological properties, such as viscosity and gel strength, and exhibit a low rate of filtration or fluid loss.
Since asphalt is generally semi-solid or solid in constituency, the very nature of this material creates numerous problems in a sulfonation process. One partial solution to this problem is to utilize asphalt which will have a relatively low softening point, thereby reducing the difficulties in handling and reacting the same. However, even with lower softening point asphalts, it is necessary to mix a diluent or solvent with the asphalt prior to sulfonation. Such solvents are generally selected so as to be inert (not sulfonatable themselves) and to have low boiling points so as to permit easy removal of the solvent from the sulfonated asphalt product. However, such selection of solvent in and of itself creates problems, to the extent that vapor phases containing significant amounts of solvent are produced in the sulfonation and neutralization steps and, where the solvent is recovered from these vapor streams, the recovery system itself produces a number of vapor phases containing lesser amounts of solvent all of which are conventionally vented to the atmosphere either continuously or intervally. Accordingly, these vapor phase streams not only result in substantial losses of solvent, but create serious pollution problems when vented to the atmosphere. Such solvents are often highly flammable and, therefore, also create safety hazards if not handled properly. Difficulties are also encountered in dispersing the asphalt in the solvent, as a result of which relatively large lumps of asphalt result in plugging of flow lines in the system, and reducing the degree of contact between the sulfonating and neutralizing agents and the asphalt and, thus, lowering conversion to sulfonated asphalt product. While, as previously indicated, lower softening point asphalts are advantageous from the standpoint of ease of handling and processing, higher softening point asphalts produce a sulfonated asphalt product having superior properties for use in drilling fluids. While the sulfonation and neutralization steps can be carried out continuously, the most effective operation utilizes batch-type sulfonation and neutralization steps. The inefficiencies of batch-type operations are well known but, in the production of sulfonated asphalts, these problems are somewhat exaggerated, to the extent that many of the steps involve manual operations and control. Numerous problems are also involved in the drying of the sulfonated asphalt product. Usually such drying is performed by a series of drum-type dryers. Since such dryers are often subject to air leakage and, to the extent that significant amounts of solvent are present, safety hazards as well as less effective recovery of solvent downstream of the dryers result. Such dryers also usually include steam stripping of the feed material and, accordingly, a vapor phase containing small amounts of particle-form sulfonated asphalt are carried by the vapor phase. This vapor phase is also normally vented to the atmosphere and, thus, creates additional air pollution problems. Finally, even with the most efficient systems for solvent recovery, a vapor phase is usually produced containing small amounts of solvent, which again is normally vented to the atmosphere, thus, again creating pollution problems as well as resulting in the loss of some of the solvent.